Synthetic polyester filaments of poly(ethylene terephthalate) were suggested some fifty years ago by Whinfield and Dickson, U.S. Pat. No. 2,465,319, and have been produced commercially for some forty years, and have for many years been the most widely-used and manufactured synthetic polymer filaments, because of their advantageous properties. Currently, polyester textile yarns are used for many widely-differing articles of apparel requiring polyester yarns in several different forms, and correspondingly manufactured by different processing techniques. Broadly speaking, there are two main categories of polyester apparel yarns, namely spun yarns (from polyester staple fiber, with which the present invention is not concerned) and multifilament (continuous filament) yarns which, themselves, again comprise two main categories, i.e., textured yarns (whose filaments are crimped, usually by false-twisting, with which the present invention is not concerned) and flat (i.e., untextured) yarns. The present invention is concerned with flat multifilament polyester yarns.
Flat yarns are used in several different types of fabrics, e.g., in satins, which may be made by knitting. As was already explained some years ago by Knox, in U.S. Pat. No. 4,156,071, although the high strength of polyester filaments may be of advantage in many fabric applications, there are also certain applications for which it had previously been preferred to use yarns and filaments of lower modulus, such as cellulose acetate, in preference over conventional drawn polyester filament yarns. In other words, the high strength of conventional polyester filaments and yarns, that can be so advantageous for certain in end-uses, may have been a disadvantage for other specific end-uses.
Although many polyester polymers (including copolymers) have been suggested, the most widely manufactured and used polyester hitherto has been poly(ethylene terephthalate), which is often referred to as homopolymer. Homopolymer has generally been preferred over copolymers because of its lower cost, and also because its properties have been entirely adequate, or even preferred, for most end-uses. Homopolymer is often referred to as 2G-T. Poly[ethylene terephthalate/5-sodium-sulfo-isophthalate] copolyester has, however, also been manufactured and used commercially in considerable quantities for some thirty years, especially for staple, and such copolyester filaments and yarns were first suggested by Griffing and Remington in U.S. Pat. No. 3,018,272. A very desirable feature of this copolyester is its affinity for cationic dyes. Commercially, such copolyester, used for making continuous filaments as well as staple fibers, has contained about 2 mole % of the ethylene 5-sodium-sulfo-isophthalate repeat units, and such copolyester has often been referred to as 2G-T/SSI. An example of a prior suggestion for using spin-oriented multilobal filaments of this copolyester as a draw-texturing feed yarn is in Example VI of Duncan and Scrivener, U.S. Pat. No. 4,041,689.
Filaments of such 2G-T/SSI have also been melt-spun with 2G-T (homopolymer) filaments (referred to as cospinning) to make cospun heather yarns that can be differentially-dyed to give interesting mixed-color appearance and effects, as suggested by Reese in U.S. Pat. No. 3,593,513 and Cemel et al. in U.S. Pat. No 4,233,363. The present invention concerns new polyester heather yarns of these cationic dyeable copolymer filaments, sometimes referred to as (2G-T/SSI), mixed with the homopolymer filaments, sometimes referred to as 2G-T.